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Topic: Photosynth coordinate system

Hi,
I am looking into pointclouds derived from photosynts for further processing. I am however having a hard time understanding the coordinate system that is used in photosynth. By looking at different synths, it appears to me that the x, y, and z-axis are used in an arbitrary orientation relative to each other. Is this correct or is there a logic that I do not see?
Any help will be most welcome.

Greetings, brakar,
When Photosynth begins a reconstruction, it begins with a pair of images and iteratively adds other photos as it is capable without any real knowledge of which way is which. Somewhere in the process, the top of each image that is grouped into a cluster is queried as to which way is up and the consensus of the majority of the photos defines which way is 'up' for the point cloud, but I'm not certain if this transforms the coordinate system or not.
I'm also wondering whether you're working with synths that are less than 100% synthy and then merging all of the different point clouds together, rather than keeping them as separate pieces, independently positionable.

The binary files are named according to which coordinate system in a synth they belong to. For example, the first bin file will be named like points_0_0.bin which signifies that it belongs to the first point cloud in the synth and it is the first part of that point cloud. The point clouds are stored in groups of 5,000 points apiece and so how many pieces are in each point cloud is simply a matter of dividing the total number of points in that coordinate system by 5,000. The second piece of the first point cloud would be named points_0_1.bin and so forth.
In a 100% synthy synth, you should only have a single coordinate system, so all bin files should be merged, but where you see bin files which begin with points_1_0.bin or points_2_0.bin, etc. these will be the first piece of a second or third point cloud, if not all the images were able to be fit together.
Apologies if I'm telling you things you already know.

Most recently Cesar Lopez has talked about the benefits that using Yasutaka Furukawa's PMVS2 to densify the point cloud brings to being able to identify the geo-referenced markers.
http://www.visual-experiments.com/2010/09/23/pmvs2-x64-and-videos-tutorials/comment-page-1/#comment-885
Hopefully that sheds a little light on things. Feel free to clarify if I'm not understanding what you're asking (and Photosynth Team members, if you're reading this, please feel free to jump in and do a better job of explaining than what my limited knowledge on the subject can provide).

Nathanael, thank you very much for your reply. There were a few very interesting links that I had not come across. And no, I am not offended by being explained a few things I allready knew. (I prefere simple explanations when there is things I don't understand. When I have a general overview I can usually dig into the rest myself. I don't understand why people gets offended by being explained things in a simple way).
However, I was not able to upload images here, so I uploaded a few photos at: http://www.oversiktsbilder.no/index.php?p=1_5_testing to illustrate what I am wondering about.
In short, in photosynth; does X describe the right-hand side of the screen, Y the axix towards the person in front of the screen, Z up... or???

Thank you douglas, this is of great help. (I do have at least one pointcloud that indicates that the "Side=&gt;" and "Look^" axis are reversed from what you write, but that may have to do with other things then Photosynth. E.g. the downloader or viewer I am using).
I did however discover an error in my rotation algorithm. As soon as I have sorted that out, I will start experimenting on more pointclouds. The important thing for me to know is if there exists a "fixed" logic or not - with regard to the orientation of coordinate axis.
Thanks again,
brakar

I finally got my software to work. (Only tested on one data-set so far).
What initially fooled me was that the pointcloud viewer I used (CloudCompare) actually reversed the east coordinates, so that the pointcloud was displayed mirrored.
With regard to Photosynth coordinate system, what I found to work was;
North =&gt; (0, 1, 0)
East =&gt; (-1, 0, 0)
Elev =) (0, 0, 1)
(Which probably is the same as douglas described, map/pointcloud just rotated 180 deg about the elev/Z-axis).

Here is a link to a description of the software I am working on: http://www.oversiktsbilder.no/index.php?p=1_7
PS: it would have been nice to be able to upload images also at this forum, after all it's a forum about imagery ;-)

I just released PC-AffineTrans, which is a tool for transformation of pointclouds like the ones that can be extracted from Photosynth.
To perform the transformation one needs to identify a set of points in the pointcloud - which must be matched with points with known coordinates in another coordinatesystem. E.g. real world UTM-coordinates.
The tool can be downloaded here: www.uavmapping.com/index.php?p=1_6_PC-AffineTrans

Nate, I am well aware of Mark Willis' work related to DEM's, and yes my work is closely related to his. My work can more or less be seen as an effort to simplify some of the steps described in his tutorial found here: http://palentier.blogspot.com/2010/12/how-to-create-digital-elevation-model.html
In this regard, PC-AffineTrans might be a (simpler and faster) alternative to the JAG3D software. I am however also working on simplifications of some of the other steps as described in his tutorial, and plan to release some new tools soon. Then I will hopefulle be able to explain my ideas in a more understandable and coherent way.

Friends,
I don't understand your discussion at all. But that's because of me, I absolutely not a specialist. Nevertheless, this may be a point to take with in your discussion:
As a user I would like to know: can I see (or put) the compass points on a 360 deg panorama? Actually when I geotag a synth after uploading, I am asked to align the image with the (Bing) map, but on the panorama itself nothing changes. Especially for a viewer a compass bearing should be useful for extra orientation.

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